Concomitantly means that two things exist or happen together, and often that one comes along with the other — as part of the same change, not as a surprise extra. It is a formal, bookish word. You will meet it in careful writing, science, and official reports, almost never in a chat with friends. If a city grows fast, traffic may increase concomitantly: the extra cars travel with that growth. A treatment may help, while side effects appear concomitantly — they show up alongside it, in the same stretch of time. Though actually, this is not the same as consequently. Consequently points to a later result, a because-and-then. Concomitantly points to things moving side by side. It also means a little more than a plain “at the same time”: the two are connected, not just coincidentally on the clock. Younger speakers rarely say it out loud. If you only mean “at the same time” in daily English, say at the same time or along with it. Keep concomitantly for when you want that careful, together-and-connected feel.

伴隨地；同時發生地（書面語）